(a) Field of the Invention
The present invention relates to a vacuum fluorescent display (VFD) and, more particularly, to a vacuum fluorescent display which is provided with a metal rib for controlling thermal electrons extracted from filaments.
(b) Description of the Related Art
Generally, a vacuum fluorescent display is a display device where thermal electrons emitted from filaments are bombarded onto a phosphor layer while being controlled by a grid electrode and an anode electrode. Such a vacuum fluorescent display involves excellent visibility, wide viewing angle, low voltage driving, and high reliability.
The vacuum fluorescent displays may be formed with a diode structure, a triode structure, or a fourfold electrode structure. Among them, the triode-structured vacuum fluorescent display with filaments, anode electrodes, and control electrodes has been used most extensively.
Specifically, as shown in FIG. 1, the triode-structured vacuum fluorescent display includes a front substrate 102, a back substrate 104, and a side glass 106. A wiring layer 108 electrically interconnects the device components. An insulating layer 112 insulates a conductive layer 110 from the wiring layer 108 except the portions of through-holes to prevent unnecessary electrical shots. The conductive layer 110 makes electrical current to be flowed from the wiring layer 108 to the phosphor layer 114 via the through-holes. The phosphor layer 114 is printed at an anode electrode with a predetermined pattern. Filaments 116 are spaced apart from the anode electrode while standing in the side of the front substrate 102 to emit thermal electrons. A metal mesh-typed control electrode 118 accelerates or intercepts the thermal electrons emitted from the filaments 116.
In the above structure, when voltage is applied to the filaments 116, the anode electrode and the control electrode 118 through a lead line 120, thermal electrons are emitted from the filaments 116. The emitted thermal electrons are accelerated and diffused by the control electrode 118, and bombarded onto the phosphor layer 114 of the anode electrode, thereby producing the desired display images.
The control electrode 118 is formed with a mesh grid that has a mesh made through etching a thin metal plate based on SUS, and a support fitted around the periphery of the mesh. The support keeps the mesh to be placed at a predetermined position such that it can control the thermal electrons emitted from the filaments 116.
Accordingly, when the mesh grids 118 are mounted onto the back substrate 104, a predetermined distance should be kept between the support and the anode electrode as well as between the neighboring mesh grids 118 to make the thermal electrons to correctly land on the phosphor layer 114, and to prevent leakage of light between the neighboring phosphor layers 114. For this reason, it becomes difficult to design minute patterns or complex polygonal patterns in the vacuum fluorescent display using the mesh grid as a control electrode.
Furthermore, in the case of the mesh grid 118, the central portion of the mesh may be sunk due to thermal deformation during the manufacturing process and at use. In this case, the capacity of the mesh grid 118 for accelerating and diffusing thermal electrons is deteriorated, and hence, the neighboring phosphor layers 114 covered by the mesh grids 118 are differentiated in brightness.
Therefore, it is inevitable that the number of the supports should increase to prevent the central portion of the mesh grid 118 from being sunk. This is also an obstacle to patterning the anode electrode in a free manner.
Recently, it has been suggested that a conductive rib may be placed at the periphery of the anode electrode to function as a control grid instead of the mesh grid that involves disadvantages in structural aspect as well as in production cost.
In such a structure, as shown in FIG. 2, a conductive rib 118xe2x80x2 is provided at the periphery of the anode electrode with the conductive layer 110 and the phosphor layer 114. The conductive rib 118xe2x80x2 is formed through repeatedly printing a conductive material onto the anode electrode such that it has a thickness capable of performing the desired electron control.
The conductive rib 118xe2x80x2 is usually formed through thick-film printing. In the thick-film printing, a solution of a conductive material is printed onto the anode electrode by a thickness of 10-30 xcexcm, and dried.
Such a process is repeated three to fifteen times to thereby complete a conductive rib with a thickness of 100-150 xcexcm, and this involves troublesome and long-term works.
Furthermore, during the printing process, the conductive rib 118xe2x80x2 and the neighboring anode electrode are liable to suffer electrical short.
In addition, the gas generated from the conductive material is left within the vacuum cell while prohibiting free flow of electrons there. This causes deterioration in brightness, accompanied with decreased life span of the device.
It is an object of the present invention to provide a vacuum fluorescent display which can be fabricated through simplified processing steps while involving improved performance characteristics.
This and other objects may be achieved by a vacuum fluorescent display including a pair of substrates spaced apart from each other with a predetermined distance. The substrates form a vacuum cell by interposing a side glass. Filaments are mounted within the vacuum cell to emit thermal electrons under the application of voltage. Anode electrodes are formed at one of the substrates, each anode electrode unit having a conductive layer and a phosphor layer formed on the conductive layer. A control electrode surrounds the anode electrode to accelerate or intercept the thermal electrons emitted from the filaments. The control electrode is formed with a single-layered structure.
The control electrode may be formed with a metallic material such as stainless steel, platinum, silver and copper.
The anode electrode unit is formed with a plurality of segments, and the control electrode surrounds each segment of the anode electrode unit. The control electrode is formed with a unitary part, or in a separate manner, and has a main control part for accelerating and intercepting the thermal electrons, and a subsidiary control part for assisting the main control part in controlling the thermal electrons. The main control part surrounds each segment of the anode electrode, and the subsidiary control part is formed at a top end portion of the main control unit in a body. The subsidiary control part is formed with an extension where the top end portion of the main control unit is extended toward each segment of the anode electrode perpendicular to the main control member.
Alternatively, the subsidiary control part may be formed with a connector interconnecting top ends of the main control part such that the connector crosses each segment of the anode electrode.
A subsidiary control electrode based on a mesh grid may surround one or more of the control electrode units.